Latching devices for the enclosure door on pad-mounted transformers and other similar equipment (collectively referred to herein as “transformers”) having a handle and locking and latching mechanisms are well known in the art. Typically, the handle as well as the locking and latching mechanisms of the latching device are located near the bottom of the transformer, close to the ground. There are often long periods in which the enclosure door is not opened, and dirt, snow, road salts, sand, insects, grass, rocks and other debris or vegetation may pile up, grow or accumulate around the handle and locking and latching mechanisms. Additionally, the closer to the ground these components are located, the more exposed they are to moisture and other corrosive agents. When access is eventually required, sometimes under emergency situations, accessibility and/or the functionality of the device may be compromised. Debris or vegetation may have to be removed or dug away to gain access and the device may not operate or disengage properly due to corrosion. In addition, the lower the handle, the more bending is required for the operator to get into a position to disengage the locking mechanisms and use the handle to open the enclosure door. More specifically, operators are required to bend their backs while keeping their knees straight when opening the latching device, thus putting increased stress on the intervertebral discs in their lumbar region and increasing their risk of sciatica.
The Institute of Electrical and Electronics Engineers (“IEEE”) standards require the enclosure door on a transformer to be secured with a pad lock and a security bolt which engages a threaded receptacle, whereby the enclosure door can only be unlatched and opened after the pad lock has been removed and the security bolt unscrewed and disengaged. On the traditionally designed latching device, the security bolt is attached to the enclosure door, while the threaded receptacle is mounted on the bottom sill of the transformer. The nature of this interface between the enclosure door and sill makes it susceptible to the development of alignment issues which can sometimes prevent the security bolt from properly engaging the threaded receptacle. For example, as disclosed in U.S. Pat. No. 6,066,802, the bolt provided for locking the outer hood of the transformer is carried by a latch plate fixed to the outer hood and is adapted to be inserted in a nut carried by the bottom sill of the transformer. The aforementioned patent (U.S. Pat. No. 6,066,802) is hereby incorporated by reference.
With the traditional design of the latching device, it is possible for a unit to appear as though it is completely closed, secured and locked yet not be, thus creating security and safety issues. For example, if the security bolt is depressed and the pad lock is looped through the recess cup and locked and then the door is moved or rotated to a closed or nearly closed position, the unit could mistakenly appear to be completely closed, secured and locked, but actually be accessible by simply raising the door. In addition, because of their proximity to the ground, the locking mechanisms on the traditional designs may not be easily viewable to a utility crew during drive-by safety inspections, especially if vegetation is overgrown or if debris has piled up or accumulated near the base of the transformer.
Some inventors have attempted to address, at least in part, one or more of the above-described problems with the traditionally designed latching device. For instance, U.S. Pat. No. 5,739,464 discloses a latching device design wherein a detachable enclosure cover is secured to the transformer via a curved latch arm mounted to the front tank panel and extending through the air or cable compartment to an opening in the front top center of the detachable cover. It is claimed that the locking structure at the juncture of the arm and the cover, in conjunction with tongue and groove structure on the tank panel and the enclosure, tightly secures the cover so that tamper resistance is improved. However, because the enclosure is a detachable cover which must be lifted and removed completely, as opposed to a rotating hinged door which remains attached to the transformer, this invention is only feasible if the cover is constructed of lightweight material, such as fiber or plastic, but steel is the traditional, and in fact preferred, material for almost all electrical utility applications. As such, this invention is not a practical solution for most of the industry because the weight of a detachable cover made of steel would make it unmanageable and unsafe. Also, the latch arm extending through the air or cable compartment can get in the way of cables. The aforementioned patent (U.S. Pat. No. 5,739,464) is hereby incorporated by reference.